Extra 1/2 serving adds more than 1/2 points?

Hey there! I have been on this forum for a while but this is my first time trying weight watchers. I've just signed up today so this is all very new! Anyways, I decided to make a salad for lunch and was entering the lite ranch. It said that one serving is 2 points. I decided that I wanted 1.5 servings. I assumed that 1.5 servings would be 3 points...and that 2 servings would be 4 points. However, when I looked on the tracker it said 1.5 servings are 4 points and 2 servings are 5 points. Typically one would think that 2 servings would be exactly twice as many points. Have you found this to be common with a lot of food points?

I've found it to be the case at times both ways - up more than doubles it and down doesn't quite halve it. I assume it's because sometimes one measurement is right at the top range of what could be two points but doubling that puts it out of the four-point range and into the five point range when the carbs/fat/fiber/protein are all factored in, and the same in reverse for going down. But with the 49 extra points/week, they get us pretty well set up so I track it as they figure it.